A very powerful tool for system admins in a Windows environment is the use of GPOs, short for Group Policy Objects. Group Policy provides centralized management and configuration of operating systems, applications, and users’ settings. They are typically stored in binary format in the SYSVOL volume. You can edit them using Microsoft Management Console (MMC) Policy Editor (gpedit.msc).
The GPO can be associated with one or more of the Active Directory containers, such as sites, domains, or organizational units (Ous). In a large environment that exists for many years, there will likely be policies that are no longer used. Finding these unused objects is not straightforward. You could do it by checking if they are linked to containers anywhere in the AD, using the Policy Editor. Depending on the size of your AD, this will take some time.
The following Powershell command will do the same much faster. It will provide a list of unused GPOs because they are not linked to anything in the AD. There is no action attached to it, so it is still up to you to look into them and, if you want, delete them.
Get-GPO -All | Sort-Object displayname | Where-Object { If ( $_ | Get-GPOReport -ReportType XML | Select-String -NotMatch "<LinksTo>" ) {$_.DisplayName } }